J. Van Acker

Optimisation of a two-stage heat treatment process: durability aspects

Heat treatment of wood at relatively high temperatures (in the range of 150–280°C) is an effective method to improve biological durability of wood. This study was performed to investigate the effect of heat treatment process optimisation on the resistance against fungal attack, including basidiomycetes, molds and blue stain fungi. An industrially used two-stage heat treatment method under relatively mild conditions (<200°C) was used to treat the boards. Heat treatment of radiata pine sapwood revealed a clear improvement of the resistance against the brown rot fungi Coniophora puteana and Poria placenta. Increasing process temperature and/or effective process time during the first process stage, the hydro thermolysis, appeared to affect the resistance against C. puteana attack, but the effect on the resistance against P. placenta was rather limited. Heat treated radiata pine showed a limited resistance against the white rot fungus Coriolus versicolor and process variations during the hydro thermolysis stage appeared not to affect this resistance. A clear difference between the resistance of heat treated Scots pine sapwood and heartwood against fungal attack is observed. Scots pine heartwood showed a higher resistance against C. puteana and P. placenta but also against the white rot fungus C. versicolor. Similar results were obtained when heat treated birch was exposed to brown and white rot fungi. Heat treatment showed an improved resistance against C. puteana attack, especially at higher temperatures during the hydro thermolysis stage. A clear improvement of the durability was also observed after exposure to the white rot fungus C. versicolor and especially Stereum hirsutum. Increasing the process temperature or process time during the hydro thermolysis stage appeared to have a limited effect on the resistance against C. versicolor attack. Heat treated radiata pine and Norway spruce were still susceptible to mold growth on the wood surface, probably due to the formation of hemicelluloses degradation products (e.g. sugars) during heat treatment. Remarkable is the absence of blue stain fungi on heat treated wood specimen, also because the abandant blue stain fungi were observed on untreated specimen. Molecular reasons for the resistance of heat treated wood against fungal attack are discussed in detail contributing to a better understanding of heat treatment methods.

MICROSTRUCTURAL AND PHYSICAL ASPECTS OF HEAT TREATED WOOD. PART 1. SOFTWOODS

Heat treatment of wood is an effective method to improve the dimensional stability and durability against biodegradation. Optimisation of a two-stage heat treatment process at relatively mild conditions (<200°C) and its effect on the anatomical structure of softwoods were investigated by means of a light and scanning electron microscopic analysis. Heat treatment did have an effect on the anatomical structure of wood, although this depends on the wood species considered and on the process method and conditions used. Softwood species with narrow annual rings and/or an abrupt transition from earlywood into latewood were sensitive to tangential cracks in the latewood section. Radial cracks occurred mainly in impermeable wood species such as Norway spruce, caused by large stresses in the wood structure during treatment. Sapwood of treated pine species revealed some damage to parenchyma cells in the rays and epithelial cells around resin canals, whereas this phenomenon has not been noticed in the heartwood section. Treated radiata pine resulted in a very open and permeable wood structure limiting the applications of this species. Broken cell walls perpendicular to the fibre direction resulting in transverse ruptures have been noticed in treated softwood species. This contributes to abrupt fractures of treated wood as observed in bending tests which can lead to considerably different failure behavior after impact or mechanical stress. In some treated softwood species maceration (small cracks between tracheids) was noticed after heat treatment. Heat treatment did not cause damage to the ray parenchyma pit membranes, bordered pits and large window pit membranes; the margo fibrils appeared without damage. Compared to the other softwood timbers tested European grown Douglas fir was the timber that stands heat treatment the best

The 600 yr eruptive history of Villarrica Volcano (Chile) revealed by annually laminated lake sediments

Lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment, and they provide unique records of the recurrence interval and magnitude of such events. This study uses a multilake and multiproxy analytical approach to obtain reliable and high-resolution records of past natural catastrophes from ~600-yr-old annually laminated (varved) lake sediment sequences extracted from two lakes, Villarrica and Calafquen, in the volcanically and seismically active Chilean Lake District. Using a combination of micro–X-ray fl uorescence (µXRF) scanning, microfacies analysis, grain-size analysis, color analysis, and magnetic-susceptibility measurements, we detect and characterize four different types of event deposits (lacustrine turbidites, tephra-fall layers , runoff cryptotephras, and lahar deposits) and produce a revised eruption record for Villarrica Volcano, which is unprecedented in its continuity and temporal resolution. Glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote Carran–Los Venados volcanic complex, Quetrupillan Volcano, and the Huanquihue Group in the studied lake sediments. Time-series analysis shows 112 eruptions with a volcanic explosivity index (VEI) ≥2 from Villarrica Volcano in the last ~600 yr, of which at least 22 also produced lahars. This signifi cantly expands our knowledge of the eruptive frequency of the volcano in this time window, compared to the previously known eruptive history from historical records. The last VEI ≥2 eruption of Villarrica Volcano occurred in 1991. Based on the last ~500 yr, for which we have a complete record from both lakes, we estimate the probability of the occurrence of future eruptions from Villarrica Volcano and statistically demonstrate that the probability of a 22 yr repose period (anno 2013) without VEI ≥2 eruptions is ≤1.7%. This new perspective on the recurrence interval of eruptions and historical lahar activity will help improve volcanic hazard assessments for this rapidly expanding tourist region, and it highlights how lake records can be used to signifi cantly improve historical eruption records in areas that were previously uninhabited.

Biological durability of wood in relation to end-use

The determination of biological durability of wood is an issue requiring sufficient reliability regarding end-use related prediction of performance. Five test institutes joined efforts to check standard test methods and to improve methodology and data interpretation for assessment of natural durability of timber species. A range of softwood and hardwood species was tested using both basidiomycete and soil soft rot testing. Based on combined processing of all data collected, an improved and simplified durability classification system was established. The test methods and the interpretation of results are proposed to be used to assess suitability and service life for applications under European hazard class 3 and 4. The methodology for basidiomycete testing only requires two test fungi and allows direct classification based on median mass loss, while for soil bed testing, which is only required when hazard class 4 applications are envisaged, a slightly more complicated approach proved to be necessary mainly due to variation in test soil parameters. Since service life can be based on natural durability classes, it is evident that these are identified differently for uses in or out of ground contact and for softwoods or hardwoods

Biological durability of wood in relation to end-use - Part 1. Towards a European standard for laboratory testing of the biological durability of wood

The determination of biological durability of wood is an issue requiring sufficient reliability regarding end-use related prediction of performance. Five test institutes joined efforts to check standard test methods and to improve methodology and data interpretation for assessment of natural durability of timber species. A range of softwood and hardwood species was tested using both basidiomycete and soil soft rot testing. Based on combined processing of all data collected, an improved and simplified durability classification system was established. The test methods and the interpretation of results are proposed to be used to assess suitability and service life for applications under European hazard class 3 and 4. The methodology for basidiomycete testing only requires two test fungi and allows direct classification based on median mass loss, while for soil bed testing, which is only required when hazard class 4 applications are envisaged, a slightly more complicated approach proved to be necessary mainly due to variation in test soil parameters. Since service life can be based on natural durability classes, it is evident that these are identified differently for uses in or out of ground contact and for softwoods or hardwoods

The Significance of Accelerated Laboratory Testing Methods Determining the Natural Durability of Wood

Summary Under laboratory conditions basidiomycete and soft rot tests were carried out on more than 20 hardwood species and 3 softwood species together with reference species to evaluate their natural durability according to the European standard EN 350 part 1. The basidiomycetes tests were carried out using Gloeophyllum trabeum, Coniophora puteana, Poria placenta and Coriolus versicolor, all fungal strains in malt agar tests and in agreement with the EN 113. Such tests did not provide a solid basis to classify all wood species according to known durability classes (EN 350, part 2). There was only a distinct differentiation noted between those species belonging to the group with a durability classified 1 to 3 and those classified 4 to 5. Conclusively, only limited additional information on durability of tropical hardwoods was gained from brown rot tests. Despite both types of laboratory tests on soft rot, prescribed in ENV 807 (vermiculite and soil) which show the essential differences to the basidiomycete test results, it has not been possible to classify the durability subdivisions in a more substantial way. Adding to these tests the durability classification, based upon a field stake test (EN 252) and a greenhouse accelerated stake test, was also carried out. Using this last method, results can be gathered more rapidly and consequently confirm the efficiency of lab tests. Generally it is perceived that lab tests and accelerated tests are important tools in the prediction of the natural durability of wood. To further improve the predictability value, durability testing would be enhanced when using a hazard class orientation. Therefore the function of the conclusive end product can be identified in a more obvious way.

Quantitative measurement of the penetration of water-borne coatings in wood with confocal lasermicroscopy and image analysis

Due to European environmental regulations, solvent-borne wood coating systems have to be replaced by water-borne and high solid coatings. Thorough research is yet needed to replace the traditional solvent-borne systems by water-borne paints and stains for exterior wooden joinery. In this article the penetration of paint primers and wood stain base-coats (solvent-borne and water-borne as well as high solids and hybrid systems) in wood is discussed. Penetration is an important factor for the durability of a coating and thus the protection of the wood. For the image capturing a confocal scanning lasermicroscope (CSLM) was used. Penetration was measured using two methods. Further statistical analysis was done to determine the factor that influenced the penetration the most.ZusammenfassungGemäß europäischer Umweltverordnungen müssen Farben auf Lösemittelbasis durch Anstriche mit Wasser als Lösemittel und hochfestem Anstrich ersetzt werden. Gründliche Forschung ist jedoch notwendig, um die traditionellen Systeme auf Lösemittelbasis zu ersetzen durch wasserlösliche Anstriche und solche für Außenverwendung. In diesem Beitrag wird die Eindringtiefe der Grundierungen und Anstrichsysteme in Holz diskutiert (Anstriche auf Lösemittelbasis, wasserlösliche Systeme sowie hochfeste und Hybridsysteme). Eindringtiefe ist ein wichtiger Faktor für die Dauerhaftigkeit einer Farbschicht und somit für den Schutz des Holzes. Für die Bilderzeugung wurde ein konfokales Lasermikroskop verwendet. Die Eindringtiefe wurde unter Anwendung zweier Methoden gemessen. Weitere statistische Analysen wurden durchgeführt, um den Faktor zu bestimmen, der die Eindringtiefe am stärksten beeinflusste.

Effect of a two-stage heat treatment process on the mechanical properties of full construction timber

Abstract This study investigated the impact of an industrially used two-stage heat-treatment method on the mechanical properties of full construction timber. Bending tests of full-size Norway spruce posts demonstrated changes due to heat treatment, such as a decrease in the density and bending strength, as well as an increase in the modulus of elasticity (MOE). The variability in bending strength and MOE appeared to be higher for treated posts and as a result the 5% values decreased, especially for the bending strength. The MOE was dependent on density for both treated and untreated posts, but this was not so for the bending strength. There appeared to be a relationship between the bending strength and the MOE, although it was rather weak, especially for treated posts. It was difficult to correlate the occurrence of natural defects in treated Norway spruce posts with an effect on the mechanical properties. Only a combination of several defects, such as large knots, enclosed pith and a deviating slope of grain, appeared to decrease the bending strength and MOE of treated posts, at least more than for untreated posts. The effect of a three year period of outdoor exposure on the strength properties of heat-treated terrace planking was limited. In particular, for the 5% value low strength range, where wood defects strongly determine the mechanical properties of wood, a three-year outdoor exposure did not change the bending strength or MOE of heat-treated wood.